Recently, we have put forward a hypothesis that the low pH compartment at the surface of he intestine facilitates micellar dissociation and allows fatty acid uptake from a micellar solution. We demonstrated that a low pH compartment on the surface of the intestine is related to the presence of intestinal mucus. This proposal is to extend our study to define the role of mucus in maintaining an acidic microclimate. Most of the studies in the literature dealth with a very specifically defined subfraction of the mucus, namely mucin or glycoproteins. We suggest that mucus instead of the purified mucin has a major functional importance. In this study, we plan to isolate the mucus from rat intestine and to study its physical and chemical properties and its effect on the transport. Our preliminary studies indicated that mucus contains heterogenous groups of materials and has the properties of polymorphism. The polymorphic properties of mucus allows it to exist in three different forms, i.e., insoluble, gel, and soluble, phase. We postulated that the polymorphic properties of the mucus are the result of aggregation or dissociation of small molecular weight components found in the mucus. These interactions may have major impacts on the function of the mucu. It is essential that one understand these unique, properties of muscus before making any attempts to study its function. In this proposal, the PI intends to use several methodologies in the study. These methodologies include chromatography, gradient ultracentribfugation and electrophoresis, as well as those developed in our laboratory, such as phase transition and reverse phase transition. We hope that these methods will allow us to study the relationships between the chemica structure and the physical properties of the mucus as well as the purified mucin. We propose to use the principle of phase transition to obtain muscus and study the interaction. If factors leading to phase transition can be defined, one can study the function of mucus under a better defined condition. If one gains a better insight into the structure and function of the mucus and mucin, their importance in normal and diseased conditions can be better appreciated.